FIG. 1 illustrates a known spectrum of a DSS sequence, which consists in NRZI form of a repeated 24 bipolar-symbol pattern as follows:p24={+1+1+1+1+1+1+1+1+1+1+1+1−1−1−1−1−1−1−1−1−1−1−1−1}.
This data set separator sequence can thus be regarded as a periodic square wave s(t) with a period 24T, where T denotes the symbol duration. A Fourier transform of this square wave is given by the following equation (1):
                                                        S              ⁡                              (                f                )                                      =                                          ∑                n                            ⁢                                                S                  n                                ⁢                                  δ                  ⁡                                      (                                          f                      -                                              n                                                  24                          ⁢                          T                                                                                      )                                                                                ,                                          ⁢          with                ⁢                                  ⁢                              S            n                    =                      {                                                                                                      sin                      ⁢                                                                                          ⁢                                              c                        ⁡                                                  (                                                      n                            /                            2                                                    )                                                                                                                          n                                                        odd                                                                                        0                                                        n                                                        even                                                              .                                                          (        1        )            
Hence, S(f) represents a line spectrum that is nonzero at odd frequencies and decreases in magnitude as 1/f.
The data set separator sequence illustrated in FIG. 1 has been used for an equalizer computation in read channels of tape-drive systems. However, such previous uses of the data set separator sequence for an equalizer computation has proven to be suitable for targets with low-order polynomials (e.g., (1-D2) PR4 polynomial) and has proven to be unsuitable for targets with high-order polynomials (e.g., (1+2D-2D3-D4)EEPR4) and general polynomials used in noise-predictive maximum-likelihood detection systems. In view of the fact that high-order polynomials and general polynomials used in noise-predictive maximum-likelihood detection systems are needed in high-performance/high-capacity tape systems, where the need exists to achieve a better match of the target characteristic to the physical channel characteristic, a challenge for the media storage industry is to improve upon the use of data set separator sequence for an equalizer computation in read channels of tape-drive systems.